The present invention relates to a road marking device which is installed as a center line, an edge line, a stop line and a crosswalk line, for the purpose of calling attention of drivers and pedestrians and guiding their line of vision. The present invention also relates to a self-luminous marking system for giving such marking.
An example of road marking devices includes an embeddable self-luminous road stud. This type of road stud comprises a transparent element made of a synthetic resin lens (e.g. polycarbonate), and a luminous unit which is disposed below the transparent element and composed of an illuminant and a condenser. The illuminant emits light when it receives a power supplied by the condenser, and the emitted light is transmitted and outwardly radiated through the transparent element. Where such road studs define the center line of a road, the center line is illuminated to help the driver who travels at night or in a tunnel.
As prior art, Japanese Patent Application Laid-open No. H8-189016 (JP-A-189016/1996) describes a method of equipping a road stud base with a transparent element made of a synthetic resin lens. Specifically, bolt holes are formed along the edge of the transparent element, while corresponding bolt holes are provided in the metal road stud base to be buried underground. The transparent element is directly fixed on the road stud base by screwing a bolt through each bolt hole.
In the road marking devices such as self-luminous road studs and self-luminous signs, an illuminant is designed to emit light by a conventional self-luminous marking system shown by the block diagram in FIG. 12.
When utilized in the road marking device, this system detects the illuminance in the road environment and properly controls the illuminant so as to emit light at a required brightness. Traditionally, the illuminance is detected with the use of a solar battery output or a general illuminance sensor available on the market.
In this system, a battery 125 or a solar battery 126 is commonly used as the power source. The solar battery 126 is accompanied by a secondary battery 127 for charging an electromotive force generated in the daytime. On the contrary, the output of the solar battery 126 drops during the night, when no light is incident on the solar battery 126 and no electromotive force is produced. Based on the output of the solar battery 126, a day/night discrimination circuit 123 decides that the illuminance in the road environment corresponds to that of xe2x80x9cNIGHTxe2x80x9d. Then, an LED drive circuit 122 is activated to supply a power from the secondary battery 127 to an LED 120, via a power supply circuit 124. The LED 120 emits light as a consequence.
In contrast, when the battery 125 is used alone in lieu of the solar battery 126, an illuminance sensor 121 is additionally disposed. The illuminance sensor 121 detects the illuminance in the road environment, and the day/night discrimination circuit 123 decides the road environment based on the detected output. When judged as xe2x80x9cNIGHTxe2x80x9d, the LED drive circuit 122 is activated to supply a power from the battery 125 to the LED 120 via the power supply circuit 124, thereby allowing the LED 120 to emit light.
With regard to the former of the above-mentioned prior art technologies, there are some problems concerning the manner of mounting the transparent element made of a synthetic resin lens on the road stud base.
In detail, the transparent element is weaker under stress than metals. Accordingly, where the transparent element is directly bolted on the road stud base, the synthetic resin lens may be subjected, along the bolt holes, to an excessive stress caused by the impact of travelling vehicles or the like. Under such stress, the transparent element may be cracked and broken. Besides, cracking may happen also due to the thermal hysteresis resulting from the difference of summer and winter temperatures.
As for the self-luminous marking system described in the latter of the prior art technologies, the system has to include an exclusive illuminance sensor unit, or an additional member or element in either respect. It is therefore difficult to minimize the size of the device or to reduce the cost through rationalization. Particularly, use of a general illuminance sensor involves problems concerning its installation position, increase in the design processes and the number of parts, and inevitable rise of costs.
In order to solve these problems, the present invention intends to provide a road marking device which has a waterproof mechanism and which prevents damage of the transparent element in the best possible way. The present invention further intends to provide a self-luminous marking system which can realize miniaturization of the device and cost reduction.
In order to solve the above problems, a road marking device of the present invention comprises: a tubular, bottomed casing which has an open top end; a cover mounted over an opening in the casing and having a window; a self-luminous marking system composed of a condenser housed in the casing, an illuminant which emits light by receiving a power supplied from the condenser, and a circuit for driving the illuminant; and a transparent element which transmits and outwardly radiates the light emitted from the illuminant. The transparent element is fixed between the cover and the casing which cooperatively hold a periphery of the transparent element, and a part of the transparent element protrudes outwardly from the window in the cover.
In this arrangement, the transparent element is securely mounted between the cover and the casing which cooperatively hold the periphery of the transparent element, without using a screw or bolt which penetrates through the transparent element. In this structure, the transparent element is free from local stresses such as impacts or deflection. The resulting road marking device is prevented from cracking and exhibits a remarkable durability.
Besides, since the cover envelops most of the transparent element, this structure imparts a protective function for the transparent element which has an insufficient mechanical strength.
In the above arrangement, the casing may be provided with an edge which outwardly and horizontally projects from a top end periphery of the casing, and a vertical wall which vertically extends from a certain portion of the edge as formed along a whole circumference thereof. Further, the cover may have a bent wall which can be closely attached to an external circumference of the vertical wall. While the external circumference of the vertical wall is closely attached to the bent wall, the casing is capped with the cover, and the transparent element is fixed in a clamped manner by the edge, an internal circumference of the vertical wall and the cover which cooperatively hold a periphery of the transparent element.
Further in the above arrangement, a packing material may be inserted between an external circumferential wall of the transparent element and the vertical wall, such that the transparent element presses on the vertical wall with interposition of the packing material. Alternatively, such packing material may be inserted in a recess formed in the external circumferential wall of the transparent element, such that the transparent element presses on the vertical wall with interposition of the packing material.
This structure hermetically seals the casing by shutting off the communication between the inside and the outside of the casing, which results in satisfactory waterproof property. This arrangement assures stronger engagement between the transparent element and the casing, while maintaining the waterproof function. Consequently, it is possible to accomplish an excellent combination of the illumination function and the waterproof function.
To fix the cover on the casing, any of the following structures can be optionally utilized. First, a screw groove is formed in each of an external circumferential surface of the vertical wall and an internal circumferential surface of the bent wall, wherein these screw grooves are engaged with each other. Second, a recess is formed in at least either of an external circumferential surface of the vertical wall or an internal circumferential surface of the bent wall, wherein a packing material is inserted in the recess. Third, a ridge is formed on each of an external circumferential surface of the vertical wall and an internal circumferential surface of the bent wall, in a mutually engageable relation, wherein the ridges are engaged with each other. Fourth, each of the vertical wall and the bent wall has a bolt hole, with the bolt holes communicating with one another when an external circumferential surface of the vertical wall is closely attached to an internal circumferential surface of the bent wall, wherein a bolt is screwed into these bolt holes. Fifth, each of the edge and the bent wall has a bolt hole, with the bolt holes communicating with one another when a top surface of the edge is closely attached to a bottom end surface of the bent wall, wherein a bolt is screwed into these bolt holes. And sixth, the cover is equipped with a flange which projects outwardly and horizontally from a bottom end of the bent wall, and a spring steel is provided for tightly clamping the flange and the edge.
Where the cover is fixed on the casing according to any of the above structures, the transparent element, which is accommodated therein and free from a stress load, can maintain its mechanical strength in a simple manner.
A self-luminous marking system of the present invention comprises: a first LED which emits light when a quantity of light in a road environment is less than a predetermined level; a battery for supplying a power to the first LED; a drive circuit for controlling a drive of the first LED; a second LED utilized without application of voltage so as to generate an electromotive force in response to an incident light; a light quantity discrimination circuit which determines, based on the electromotive force generated by the second LED, whether the quantity of light in the road environment is less than the predetermined level; and a switch circuit which controls an operation of the drive circuit, based on a result determined by the light quantity discrimination circuit.
Preferably, the light quantity discrimination circuit starts to operate, when the second LED continuously generates an electromotive force for a given time in response to the incident light.
In the above self-luminous marking system, the battery may be replaced with a solar battery and a condenser element.
Given that an LED is a crystal having an p-n junction, the second LED is used without application of a voltage. As a consequence, when a light is incident on the second LED, a free electric charge is generated and transformed into an electric energy, thereby producing an electromotive force. Judging from the electromotive force, if the quantity of light in the road environment is lower than the predetermined level, the first LED is activated. A series of these operations proceeds automatically.
Further, it is desirable to utilize the self-luminous marking system of the present invention, in connection with the road marking device of the present invention as mentioned earlier.